I sold electronics since 1990, and left the business in 2009.
I have 2 published Theater Rooms to my credit, one was my own that I conceived, constructed, and executed myself, the other one was for a client. A friend kicked in the theater themed carpet I selected, but I did everything else.
So I have a deep although dated knowledge base of audio/video.
Regarding 4K....
Broadcast material is generally governed by the federal communications commission. A few years ago they revised the broadcast regulations, and that was the end of the over the air analog system, and the beginning of over the air digital broadcasting. Along with the host of standards, in typical federal government style (pages and pages) came the resolution standards. Those play a large part in the resolution of video material for broadcast. The work around that allows for more advanced resolutions like 4K is pay programming. A broadcast media like DirecTV, Firestick, Roku, etc can broadcast in 4K because it is a paid subscription.
That is a big reason why there is limited 4K material.
In order for higher resolution video to become more readily available, the FCC had to update the broadcast standards.
All of that info is off the top of my head.
For more information, especially about 4KTV, read this:
https://www.theverge.com/2017/2/2/14488608/4k-tv-broadcasts-ajit-pai-atsc-3-hdr